Communication system



Patented Mar. 3, 1936 UNITED STATES PATENT OFFICE 2,032,725 COMMUNICATION SYSTEM Application December 16, 1933, Serial No. 702,751

10 Claims.

My invention relates to communication systems, and particularly to systems for communicating between two spaced locations on a train. A feature of my present invention is the pro-' vision, in systems of this type, of apparatus which permits of both automatic control and telephone communication. A further feature of my invention is the provision of apparatus for establishing a characteristic frequency for each train of a railway division, all similarly equipped. A still further feature of my invention is the provision of apparatus wherewith the equipment at the two locations may be set to respond only to each other, wherebya non-interfering system for each train of a railway is obtained. 'Other features and advantages of my invention will appear as the specification progresses.

I will describe oneform of apparatus embodying my invention, and will then point out the novel features thereof in claims.

In the accompanying drawings, Figs. 1 and 2 when taken together constitute a diagrammatic view of one form of signaling apparatus embodying my invention. The apparatus of Fig. 1 is that installed at the location of the supervising operator, which, in this instance is on the locomotive. The apparatus of Fig. 2 is that installed at another location on the train. While the apparatus of Fig. 2 may be installed at any point on the train, it will be referred to in the following description as being mounted in the caboose of a freight train. The communication circuit from one end of the train to the other may take different forms and preferably includes the traffic rails in the manner described and claimed in the L. O. Grondahl application, Serial No. 450,135, filed May 6, 1930, on Electric train signaling systems. 1

Systems have been proposed for telephoning between two spaced locations on a train, or between two trains, or between a wayside station and a train by transmitting from one location to the other a single side band of a carrier current modulated by the voice frequencies. In

my present systeml propose to combine with such telephone system an automatic brake control which is normally active and which automatically transmits between the two locations control impulses consisting of a side band frequencyof the carrier modulated by apredetermined intermediate frequency within a voice frequency range and which intermediate frequency has itself been first modulated with a desired control frequency preferably below the voice frequency range. That is to say, the carrier current during auto matic control is double modulated. The receiving equipment is effective to demodulate the transmitted side band and to also detect the control frequency. when telephone communication is established, the control apparatus is 5 rendered inactive and the carrier is modulated by the voice frequencies, the control condition in effect previous to the establishing of telephone communication being maintained unchanged. By such double modulation of a carrier current a relatively large number of trains of a railway, all similarly equipped, can each be provided with a control system having a distinctive frequency channel without a changeof the carrier fre-- quency and with comparatively simple .and reliable apparatus. This double modulation of the -carrier is in effect a shifting of the carrier frequency.

Although I am here disclosing a specific embodiment of my invention, it will be understood that I do not wish to limit myself to brake control and telephone communication. My invention is equally useful to systems wherewith the operator of a leading locomotive governs the operation of a helper locomotive. Furthermore, it will be understood that the automatic control may be used without the telephone equipment and that my invention is also equally useful for signaling from a wayside station to a train.

In each of the two views like reference characters refer to similar parts.

Referring to Fig. 1, the reference character EV designates the usual engineer's brake valve of standard type capable of establishing the release, running, lap, service and emergency conditions of the brake pipe pressure. A circuit controlling contact assembly designated as a whole by the reference character CA is associated with the brake valve EV. As shown schematically, a contact member 4 is operatively con- 40 nected with the brake valve handle 5 and is adapted to engage an arcuate contact 6 in both the release and rimning positions of the handle 5, a contact I in the lap position and an arcuate contact 8 in both the service and emergency positions of the handle 5. This contact assembly also includes a manually operated push button PB adapted to normally close a contact 9 and 'to close a contact Ill when depressed, the push button being of the spring return type.

Located on the locomotive is a generator GI of alternating current adapted to supply different frequencies in accordance with the different positions of the contact assembly CA. As here shown,

this generator GI 'is of the vacuum tube type and comprises an electron tube 3| and its associated circuits. The tube 8| contains the usual heated filament |'2, a grid l3 and a plate l4, one side of the filament being preferably connected with a ground electrode 36. The tube BI is provided with a plate circuit including an iron core reactor I5 and a source of current not shown, the positive terminal of which source is indicated at B and the negative terminal of which is grounded for completing the plate circuit through the ground electrode 33. The tube BI is also pro'vided with a grid circuit including a condenser- 31, a grid leak unit I, a coupling condenser l1 and a tuned oscillating circuit consisting of the primary winding I3 of a transformer TI and a suitable condenser 20, 22, 23 or 24, to be inserted into the circuit in accordance with the position of the contact assembly CA. Condensers 20, 22, 23 and 24 are of different capacities and are adapted to be inserted into the oscillating circuit in the following manner. With the handle 5 set at either the release or running position and the contact member 4 engaging the contact 8, this oscillating circuit can be traced from the lower terminal of the primary winding I8 along wire l9, condenser 20, contact 6, contact member 4, contact 9 of the push button PB and wire 2| to the top terminal of the primary winding l3. With the handle 5 moved to the lap position and the contact member 4 engaging the contact I, the condenser 22 is inserted into this oscillating circuit, and with the handle 5 moved to either the service or emergency positions, the

condenser 23 is selected. Depressing the push button PB at any time connects the condenser 24 with the oscillating circuit. It will be assumed that the condenser 20 has such capacity as to produce oscillations of a frequency of 20 cycles per second, the condenser 22a frequency of 30 cycles per second, the condenser 23 a frequency of 40 cycles and the condenser 24 a frequency of 10 cycles. It will be understood, of course, that other frequencies could be chosen and that the above frequencies-are given by way of illustration only.

It follows that the release and running positions of the brake valve EV are accompanied by generator GI producing a frequency of 20 cycles per second, the lap position of the valve is accompanied by a frequency of 30 cycles per second, the service and emergency positions of the valve by a frequency of 40cycles and that the depressing of the push button PB at any time is accompanied by the generator GI supplying a curent of 10 cycles per second. In each case an electromotive force of corresponding frequency. will be induced in the secondary winding 25 of the transformer TI. The function of these several low frequency currents supplied by the generator GI in accordancewith the position of the brake valve EV and the push button PB will appear hereinafter.

The equipment of Fig. 1 includes a three -position master switch MB. This master switch MS is manually operated to any one of three positions indicated on the drawings by the numerals 1, 2 and 3. The position No. 1 is the normal position to which the switch returns under the action of a biasing spring not shown when not actually held manually in one of the other two positions. When the switch occupies its No. 1 position, automatic control of the train brakes is effected, as will appear as the specification progresses. The No, 2 position is used when it is desired to transmit a telephone message from the locomotive, and'the No. 3 position is used when it .is

desired to receive a telephone message on' the locomotive. Consequently, the locomotive equipment can be shifted to any one of the three conditions, automatic brake control. speech sending or speech receiving at the discretion of the locomotive operator.

The equipment of Fig. 1 also includes a manually operated selector SI. As shown schematically, two manually operated contact members 4| and H are connected together for being actuated in step with each other and are adapted to be set in any one of five different positions as will be understood by an inspection of Fig. 1.. Associated with the contact me'mber 4| are five condensers 34*, 34 34, 34 and 34, of different capacities which are selected according to the position of the member 4|. In like manner the contact member 1| selects any one of five condensers 12*, 12", 12, '12 and 12 of different capacities according to its position. As will appear hereinafter, the frequency channel on which a train is operated is determined by the position of the contact members 4| and H of the selector SI. Hence, in this instance, any one of live different frequency channels can be selected for the train.

Located on the locomotive is a second electron tube 26 which is adapted to at times function as an amplifier and at other times asan element of an oscillator indicated as a whole by the reference character G2. The tube 26 contains a heated filament 21, a grid 23 and a plate 23, one side of the filament being preferably connected with a ground electrode 30. A plate circuit is provided including the upper portion of the primary 'wlnding 3| of a transformer T2 and the source of current, the positive terminal of which source is indicated at B and the negative terminal of which is grounded as pointed out hereinbefore. The lower terminal of the primary winding 3| is connected. with the grid 28 over wire 40, contact 33 of the master switch MS in its No. 1 position and wire 38. In accordance with the varying position of contact member 4|, 2. different one of the condensers of the selector Si is connected, across the primary winding 3| as can be traced from the lower terminal of that winding along wire 40, contact member 4|, any one of the group of condensers 34 34 34", 34 and 34 according to the position of the member 4|, wire 44, contact 35 of the master switch MS in its No. 1 position and wire 45 to the top terminal of the primary winding 3|. By proper proportioning of the number of turns of the primary winding 3| and the capacity of the condenser 34, which is the condenser selected as illustrated in Fig. 1, this circuit system will oscillate at any suitable frequency, which I shall assume tobe 1000 cycles per second. Each of the remaining condensers 34', 34 34 and 34 is so proportioned that when inserted in the circuit with the primary winding 3| a different frequency is generated. Hence, the oscillator G2 can be made to produce any one of five different frequencies according to the setting of the contact member 4|. As stated above, I shall assume the frequency of the oscillator G2 to be 1000 cycles per second when the condenser 34 is selected as illustrated in the drawings. The other frequencies I shall assume to vary from 1000 cycles and to vary from each other by a sui'iicient number of cycles per second to provide five different frequency channels. It will be noted, however, that these several different frequencies of bscillator G2 will preferably fall within the usual 75 voice frequency band which band I shall refer to as extending from 500 to 2500 cycles.

The oscillations of the oscillator G2 are modulated by the output of the generator GI in the following manner. The secondary winding 25 of the transformer Tl has its upper terminal connected with the ground electrode 36 through a condenser 46 and has its lower terminal connected with the oscillating system over wire 41, contact 48 of the master switch in its No. 1 position, a reactor 49 and wire 50. This modulating circuit will easily be recognized as a form of the Heising modulation circuit. It follows that with the selector SI set in the position illustrated in Fig. 1 and the master switch MS occupying its N0. 1 position, the oscillator G2 supplies a current of 1000 cycles modulated at the low frequency of 10, 20, 30 or 40 cycles according to the position of the brake valve handle 5 and the push button PB, and this modulated current will induce an electromotive force of corresponding frequency in the secondary winding 5| of the transformer T2.

At other times the electron tube 26 functions as an amplifier and to this end the grid 28 of the tube 26 is provided with a circuit including the secondary winding 32 of a transformer T3 and a battery 33. The primary winding 42 of the transformer T3 is included in a circuit which also contains a battery 43, a microphone M and the contact 35 of the master switch MS when moved to its No. 2 position. It is to be seen, therefore, that when the master switch MS is shifted from its No. 1 to its No. 2 position, the tube 25 no longer functions 'as an element of an oscillating system but functions as an amplifier of the voice frequencies developed by speaking into the microphone M and applied to the grid 28 through the medium of the transformer T3, the oscillating system being now open at the contacts 35 and 39 and the modulating circuit being open at the contact 48 of the master switch. These voice frequencies will appear in the plate circuit of tube 26 greatly increased in amplitude and will induce an electromotive force of corresponding frequencies in the secondary winding 5| of the transformer T2. That is to say, with the selector Sl set in the position illustrated in the drawings and the master switch MS occupying the No. l position. there will be induced in the secondary winding 5i of the transformer T2 an electromotive force having a frequency of 1000 cycles modulated at the frequency of 10, 20, 30 or 40 cycles according to the position of the handle 5 and the, push button PB; and that with the switch MS moved to its No. 2 position, there will be induced in the secondary winding 5| an electromotive force corresponding to the voice frequencies developed in the microphone M and amplified by the electron tube 26. As stated above, these voice frequencies will be assumed to extend over a band from 500 to 2500 cycles.

The secondary winding 5| of the transformer T2 is connected with the input of a balanced modulator oscillator BMO adapted to generate a carrier frequency of say, 7000 cycles per second. This balanced modulator oscillator BMO may take different forms, such for example as two vacuum tubes connectedto oscillate in parallel, and. is here shown conventionally only for the sake of simplicity as its specific structure forms no part of my invention. A preferred type of such oscillator is described in a copending application for Letters Patent, Serial No. 658,932, filed Feb. 28, 1933, by Leland D. 'Whitelock et al for Communication systems. It is deemed suflicient for this description to say that the output of the modulator oscillator BMO contains the side bands of the modulated carrier with the carrier suppressed. Thus, the output of the modulator oscillator BMO consists of an upper side band of 8000 cycles modulated at 10, 20, 30 or 40 cycles and a lower side band of 6000 cycles modulated at 10, 20, 30 or 40 cycles during automatic control; and consists of an upper side band extending from 7500 to 9500 cycles and a lower side band extending from 4500 to 6500 cycles during telephone communication. Both the upper and the lower side band frequencies of the modulator oscillator BMO are impressed upon a filter F2 which is adjusted to pass one side band and sup press the other, the upper side band being preferably passed. The upper side band passed by the filter F2 is impressed upon the input of an amplifier transmitter AT preferably consisting of two power tubes operated in the conventional push-pull manner, and is amplified to a relatively high energy level and then passed to an output transformer T4. The specific type of neither the filter F2 nor the amplifier transmitter AT forms a part of my invention and these devices are shown by a symbol only in order to simplify the drawings as much as possible.

It follows from the foregoing description of the transmitting equipment on the locomotive that under the No. 1 position of the master switch MS the carrier current of 7000 cycles will be double modulated by the channel frequency of 1000 cycles and the signaling frequency of 10, 20, 30 or 40 cycles as the case may be. The carrierand the lower side band will be suppressed, leaving the upper side band consisting of 8000 cycles plus the signaling frequency to be delivered to the secondary winding 52 of the output transformer T4. With the mast-er switch MS shifted to its No. 2 position and the operator speaking into the microphone M, current will be transmitted to the secondary winding 52 of the output transformer T4 consisting of the upper side band of the carrier frequency plus voice frequencies, in this instance a band extending from 7500 to 9500 cycles. The setting of the selector SI to a position to select one of the other condensers 34 34 34 or 34 will change the channel frequency and in turn cause a corresponding change in the upper side band supplied to the secondary winding 52 under the control condition. The output of the secondary winding 52 will be delivered tothe communication circuit in a manner to now be described.

The reference character N designates a mechanically tuned coder. This coder N may take any one of many forms well known to the art and preferably is that disclosed in the Letters Patent No. 1,858,876, issued May 17, 1932, to P. N.

Bossart, on Coding apparatus. It is deemed sufficient for this description to say that the winding 53 of the coder N is energized from a battery 54 over its own contact 55 and as long as so energized, a contact member 56 is oscillated between two contacts 51 and 58 at a frequency of say, cycles per minute. In other words, the contact member 56 alternately makes engagement with'the contacts 51 and 58 during alternate one half second intervals.

59 and 60 are inductor coils mounted onthe locomotive in inductive relation with the traffic rails II and II, respectively, which rails are included in the communication circuit. By means of these inductor coils 59 and 60 energy is transcircuit of the transmitting equipment or to the input circuit of the receiving equipment. With the master switch MS occupying its No. 1 position, the coils 58 and 80 are connected with the secondary winding 52 of the output transformer T4 each one-half second interval the contact member 55 of coder N engages the contact 58. This circuit can be traced from the top terminal of the secondary winding 52 through a tuning condenser 52, wire 63, contact 55-58, contact 64 of the master switch, coils 50 and in series,

ground. electrode 55 and thence by a ground electrode 65 to the lower terminal of the secondary winding 52. During the half second interval that the contact'member 58 engages the contact 51 the coils 59 and 60 are disconnected from the output transformer T4 and are connected with the input circuit of the receiving equipment to be shortly described, the input circuit including a filter-Fl and a ground electrode 51, as well as the coder contact 5651 and the contact 64 of the master switch as will be understood by an inspection of Fig. 1. When the master switch MS is shifted to its No. 2 position, the contact 64 I shunts around the coder contact 5558 and the inductor coils 59 and 60 are connected directly with the output transformer T4, while, when the switch MS is shifted to its No. 3 position, the contact 54 shunts around the coder contact 56-51 and connects the coils 59 and 50 directly with the input filter Fl. It follows that under the No. 1 position of the master switch the transmitting and receiving equipments on the locomotive are alternately coupled with the communication circuit for periods of one-half second through the medium of the coder N. The transmitting equipment is continuously coupled with the communication circuit when the switch MS is shifted to its No. 2 position and the No. 3 positionof the master switch is effective to continuously couple the circuit with the receiving equipment.

In the form here shown, the receiving equipment of; Fig. 1 comprises the filter Fl, an amplifier A1, a demodulator D, a filter F3, a second amplifier A2 and an amplifier detector A3. Inasmuch as such devices are well-known to the art and the specific structure of none of them forms a part of my invention, they are each shown by a symbol only in order to simplify the drawings and make them moreleadily understood. This receiving'equipment will now be described.

The input filter Fl is preferably adjusted so as to pass a frequency band of 7500 to 9500 cycles and to attenuate all other frequencies. That is, the input filter Fl of the receiving equipment is adjusted to pass a frequency band corresponding to the upper side band of a carrier of 7000 cycles modulated by voice frequencies. In the form of my invention here shown the equipment at a location is preferably arranged to both send and receive on the same carrier frequency and also on the same channel frequency. This means that the frequency band sent out by the apparatus at the other location to be described later, and to which the receiving equipment on the locomotive is to respond is the same as that sent out by the transmitting equipment on the locomotive as previously described. The current passed by the filter Fl is impressed upon the amplifier Al which amplifies the above-mentioned frequency band and passes it on to the balanced demodulator-D where the received frequency band is combined with a carrier of 7000 cycles originating in D with the result that the output of the demodulator D contains an upper and a lower side band. The lower side band consists of the received frequencies less 7000cycles, that is, frequencies within the band between 500 and 2500 cycles. It is to be noted that this lower frequency band is the same band impressed upon the balanced modulator oscillator BMO of the transmitting equipment. The upper side band consists of the received frequencies plus 7000 cycles.

The output of the demodulator D is passed through the band pass filter F3 adjusted so as to pass the lower side band of 500 to 2500 cycles and to exclude the upper side band. The current passed by the filter F3, therefore, contains frequencies only within the voice frequency range and these frequencies are then in turn impressed upon the input of the amplifier A2 where they are caused to appear in the output of that amplifier greatly increased in amplitude.

During such time as the master switch MS occupies it No. 1 position, the output of the amplifier A2 includes a tuned circuit network and at such time as the switch MS is shifted to. its No. 3 position, the output of the amplifier A2 is connected with the operating winding of a loud speaker. This tuned circuit network canbe traced from the upper right-hand terminal of amplifier A2 along wire 68, contact 69 of the master switch MS in its No. 1 position, a reactor 10, contact member ll of the selector Sl, condenser 12, wire 11, input of the amplifier detector A3 and thence by wire 18 to the lower right-hand terminal of the amplifier A2. At such time as the master switch MS is shifted to its No. 3 position the output of the amplifier A2 includes wire 68, contact 59, operating winding of a loud speaker 13, a ground electrode 19 and thence by a ground electrode 80 and wire 18 to the lower right-hand terminal of the amplifier A2. work just traced are so proportioned and adjusted as to respond to a frequency band extending from 1010 to 1040 cycles, that is, to a band equal to the channel frequency of 1000 cycles modulated at the signaling frequencies of 10, 20, 30 and 40 cycles. The other condensers 12 12 12 and 12' associated with the contact member H are of such capacity as to causethis tuned output circuit of amplifier A2 to respond to other channel frequencies plus the signaling frequencies. The arrangement is such that preferably the condenser selected by the contact member 1| tunes this output circuitof the amplifier A2 to respond to the same channel frequency as the condenser selected by the contact member M in the same corresponding position established for the oscillator G2, it being recalled as stated above, that the equipment at a location is preferably arranged to both send and receive on the same channel frequency. The circuit including the operating winding of the loud speaker LS is non-tuned and hence all the voice frequencies passedto the output of-the amplifier A2 will be reproduced by the loud speaker LS.

The amplifier detector A3 acts as a detector of the channel frequency and also amplifies the signaling frequency component with which it is modulated, the signaling frequency being passed to the primary winding 13 of a transformer T5.

The secondary winding 14 of the transformer T is connected with tuned circuit networks 15 and The parts of the tuned circuit netoutput terminals of which are connected with the winding of a relay 82. In like manner a portion of the network 16 is connected with the input terminals of a rectifier 83, the output terminals ,of which are connected with the winding of a relay 84. The networks 15 and 16 are tuned toresonance at the frequencies of 30 and 10 cycles, respectively.

It follows from the foregoing description of the receiving equipment on the locomotive that when the upper side band of a carrier of 7000 cycles double modulated at 1000 cycles and 30 cycles is impressed upon the receiving equipment and the master switch occupies its No. 1 position, the side band is filtered, demodulated, amplified and then impressed upon a tuned circuit responsive to the frequency of 1030 cycles and which includes the input of the amplifier detector A3. The amplifier detector A3 detects the channel frequency of 1000 cycles and causes to appear in its output a fre-, quency of 30 cycles only. This signaling frequency is impressed upon the tuned circuit 15 and the relay 821s energized. In the event the channel frequency of 1000 cycles has been modulated at the signaling frequency of 10 cycles a current of 10 cycles appears in the output of the amplifier detector A3 and. the relay 84 is energized. Relay 82 controls at its front contact 85 a simple circuit for a signal lamp 86 and the relay 84 controls at its front contact 81 a circuit for a signaling device here shown as a bell 88. When the master switch is shifted-to its No. 3 position, the output of the amplifier A2 is shifted to the operating winding of the loud speaker LS and upper side band frequencies corresponding to the carrier modulated at voice frequencies impressed upon the input of the receiving equipment will be filtered, demodulated, amplified and reproduced by the loud speaker LS.

Referring now to Fig. 2, the caboose is provided with a master switch MS and a selector SI identical to the corresponding devices of Fig. 1. The caboose is also provided with transmitting and receiving equipments similar to the corresponding equipment on the locomotive. It is deemed unnecessary to repeat the description of these various devices in detail except to point out their modifications. The generator GI of the transmitting equipment of the caboose is the same as the generator GI on the locomotive except only two condensers 89 and 90, of different capacities, are provided for its oscillating circuit, the condenser 89 being normally inserted into the circuit over a normally closed contact I23 of the push button PB and the condenser 98 being connected into the circuit when the push button is depressed and its contact I24 closed. I shall assume that oscillations of 30 cycles per second are produced when the condenser 89 is included in the oscillating circuit and that the oscillations are of a frequency of 10 cycles when the condenser 98 is selected.

The electron tube 26 of Fig. 2 serves at times as an element of an oscillating system and at other times as an amplifier of voice frequencies on the caboose occupies its No. 1 position this channel frequency is modulated by the 30 or 10 cycles of the generator C fl over the modulated circuit including the contact 48 of switch MS. With the master switch MS shifted to its No. 2 position, the oscillating and modulating circuits associated with tube 26 are opened at the contacts 35, 38 and 48, and the microphone M is connected with the primary winding 42 of the associated transformer T3 and the tube 26 functions as an amplifier of the voice frequencies developed by speaking into the microphone M. Hence, electromotive forces having a frequency corresponding to the channel frequency of 1000 cycles modulated at the frequency of either 30 or cycles, or voice frequencies produced in the microphone are induced in the secondary winding 5| of the transformer T2 of the caboose transmitting equipment in precisely the same manner as induced in the secondary winding 5| of the transformer T2 on the locomotive. The secondary winding 5| of the caboose transformor T2 is connected with a balanced modulator oscillator BMO preferably similar to the corresponding device of Fig. '1. Consequently, side band frequencies of a carrier of 7000 cycles double modulated at the channel and signaling frequencies or modulated at the voice frequencies appear in the output of the modulator oscillator. The filter F2 and amplifier transmitter AT of Fig. 2 are preferably similar to the corresponding devices on the locomotive and thus there is produced in the secondary winding -52 of the associated output transformer T4 the upper side band only amplified to a relatively high energy level. The other condensers associated with the contact member 4| of the caboose selector S! are preferably of the same respective capacities as the corresponding condensers associated with the contact member 4! of the selector on the locomotive so that corresponding positions of .the two selectors cause the associated transmitting equipments to operate on like channel frequencies. The manner of transferring the energy supplied to the secondary winding 52 of the caboose output transformer T4 to the communication .circuit will be pointed out later in the description.

The filter Fl, amplifier Al, demodulator D,

band pass filter F3, amplifier A2 and amplifier detector A8 of the caboose receiving equipment, all may be and preferably are similar to the respective devices on the locomotive.

9| and 92 are inductor coils mounted on the caboose in inductive relation with the traffic rails H and ii, respectively, and these coils serve as the medium for transferring energy from the caboose transmitting equipment to the communication circuit and from the communication circuit to the caboose receiving equipment.

That the apparatus of Fig. 2 may be coupled with the communication circuit in step with the apparatus of Fig. 1, two synchronizing relays 95 and HM are controlled by the receiving equipment of Fig. 2 and in turn govern its output cirsuit in the following manner. At the start, current picked up from the traffic rails at the caboose will be impressed on the filter Fl through a circuit which can be traced from the righthand terminal of the coil 92 over contact 93 of the master switch MS in its No. 1 position, back contact 94 of the relay 95, filter Fl, ground electrode 96 and thence by ground electrode 91'to the left-hand terminal of the coil 8!. in connection with the description of the apparawe of Fig. 1, the control impulse supplied to the trafiic rails'consists of the upper side band of the carrier double modulated by the channel and signaling frequencies, and this side band when impressed upon the receiving equipment through the filter FI is filtered, demodulated and amplified and a frequency corresponding to the channel frequency modulated by the signaling frequency is made to appear in the output of the amplifier A2. Therefore, there will appear in the output of the amplifier A2 of Fig. 2 the channel frequency, in this instance 1000 cyclemmodulated by one of the signaling frequencies. This output circuit for the caboose amplifier A2 can be traced from the upper right-hand terminal of the amplifier A2 along wire 00, contact of the master switch in its No. 1 position, one side of a full-wave rectifier I00, winding of the relay III, the other side of therectifier I00, reactor II, contact member II of the selector SI, condenser 12, wire I03, input of the amplifier detector Al and thence to the lower right-hand terminal of the amplifier A2. This circuit being tuned through the medium of the reactor III and condenser I2 to respond to the channel frequency of 1000 cycles, it follows that the relay IOI will be energized. in response to this control impulse when impressed upon the input circuit. Relay III on picking up closes at its front contact I a simple circuit for the relay 0! and that relay will be energized. Relay 0! on picking 'upopens the above traced input circuit to the filter 1"I at the back contact 04 but that circuit is now completed at the front contact I 00 of the relay III and hence both relays 00 and III remain picked up as long as the incoming control current is received. It will be recalled that a control impulse is transmitted to the trafllc rails by the locomotive apparatus for a period of one-half second as determined by the coder N, and thus the relays and Ill will be energized for approximately an interval of one-half second. When the incoming impulse ceases, the relay III immediately drops but the relay ll remains picked up for an interval, approximately one-half second, inasmuch as it is slow releasing in character. During the slow release period of the retherefore, that following the receipt of an impulse of control current on the caboose the inductor coils are connected with the output of the transmitting equipment and an impulse of current consisting of the upper side band of the carrier double modulated at the frequency of 1000 cycles and 30 cycles is supplied to the trafiic rails. As soon as the relay ll releases, the transmission stops and the caboose receiving equipment is-again connected with the inductor coils 9| and 02 readytoreceive thenextlmpulsetransmitted from the locomotive. Hence. the caboose receiving and.- transmitting equipments will be alternately coupled with the communication circuit in synchronism with the locomotive equipments. It will be noted that with the master switch MS of Fig. 2 shifted to its No. 2 positlim,

xtheinductor coils ii and 02 are connectedvdirectly with the output transformer T4 over 'con-' .tact l3 and wires I02 and I20, and with the switch MS shifted to its No. a the filter FI is connected directly with the inductor coils over the contact 93.

As stated above, the output circuit for the amplifier A2 of Fig. 2 including the condenser 12 and the input of the amplifier detector A3 is so proportioned and adjusted as to respondto a .current of 1000 cycles modulated at a signaling frequency of 10, 20, 30 or 40 cycles.v The associated' amplifier detector A3 detects this channel frequency and causes to appear in its output, which includes the primary winding of an associated transformer T5, the signaling frequency only. The secondary winding 14 of the transformer T is connected with the tuned circuits I00, I09, H0 and ,I II tuned to respond to 20, 30, 40 and cycles, respectively. A portion of the circuit network I08 is connected with the top winding of a relay IIZ through a full-wave rectifier H3 and in like manner portions of the circuits I09, H0 and III are connected with relays II4, H5 and H6, respectively through the respective rectifiers Ill, 8' and II 9. Consequently, the relays H2, H4, H5 and H6 will be energized when the controlcurrent contains the signaling frequencies of 20, 30, 40 and 10 cycles, respectively.

The relays II2, Ill, II5 and H6 may be utilized for selectively governing a control and signaling mechanism in any desired manner and in the form here shown they control the different positions of an auxiliary brake controlling mechanism and a signaling device. The caboose is provided with a brake controlling mechanism including a. main reservoir MR, a feed valve FV and three electropneumatic valves RV, LV and SV; and a signaling device I26. The caboose, of course, will also be equipped with a compressor and all other apparatus necessary to insure an ample supply of air pressure in the main reservoir MR independent of the usual supply of air pressure on the locomotive. The valves RV and SV are each biased to the closed position and each is lifted to the open position when the associated magnets I20 and I2I, respectively, are energized. The valve LV is biased to the open position and is held closed when its magnet I 22 is energized. When the valve RV is open, the brake pipe BP is connected to the feed valve FV and the auxiliary brake controlling mechanism reproduces the running condition of the engineers brake valve-EV on the locomotive. When either the valve SV or LV is open, the brake pipe BP is connected to the atmosphere through a vent of such characteristics as to produce a reduction in brake pipe pressure at substantially the service rate of reduction of the usual brake valve to effect a service application of the train brakes. When the valve LV is held closed and the valves RV and SV are closed due to their bias, both .the supply and exhaust or the brake pipe are closed and the auxiliary brake controlling mechanism reproduces the lap condition of the engineers brake valve.

When the relay H2 is energized, current will flow from the positive terminal of a current source over the front contact I21 of that relay and through the magnets I20 and I22 in series to the other terminal of the current source, and both magnets I20 and I22 will'be'energized to open valve RV and to hold closed the valve LV with the result that the running condition of the brake pipe pressure will be established. When the relay Ill is energized, current will flow from the current source over the front contact I28 of that re lay and through the magnet I22 to the opposite terminal of the current source, andmagnet I22 will be energized with the result that the valve LV is held closed and the lap condition of the brake pipe pressure will be established. When the relay I I is energized, current will flow from the current source over the front contact I 29 of that relay and through the magnets I 2| and I22 in series to the opposite terminal of the current source, and these two magnets will be energized with the result that the valve LV will be closed and the valve SV willbe open and the service application condition of the brake pipe pressure will be established. In the event all three of the relays I I2, H4 and H5 become deenergized, the magnet I22 will be without current and the valve LV will be open to establish a brake applying condition of the brake pipe pressure, so as to provide the closed circuit principle for the apparatus. With the relay H6 energized, current will flow over a simple circuit including its front contact I30 and the bell I26 and the bell will be sounded. Each of the relays H2, H4 and H5 is providedwith a second winding and a stick circuit easily traced. Consequently, when the caboose operator shifts the master switch MS to either its No. 2 or No. 3 position, the contact I3I completes the connection to the current source and current will flow to the stick circuit of whichever of the relays H2, H4 and H5 happen to be energizedat the time and that relay will beheld picked up notwithstanding energy is no longer supplied over the respective tuned circuit network. The relay H6 which responds to the 10 cycle signaling current is provided with a second front contact I32-which is effective when closed to supply current to the stick circuits for the other relays I I2, I I4 and I I5. Hence, a signaling current of 10 cycles is effective to not only sound the bell I20 but to also retain energized whichever of the relays H2, H4 and H5 happen to be picked up with the result that the established condition of the auxiliary brake controlling mechanism remains unchanged.

In describing the operation of my system I shall first describe the automatic control and then point out the manner whereby the operators at the two locations may establish telephone communication. Furthermore, I shall assume that the master switches at each of the two locations normally occupy the No. 1 position and that the two selectors are set in the position illustrated in the drawings. Under these circumstances and with the brake valve handle 5 moved to either the release or running position, the generator GI on the locomotive supplies current of 20 cycles with which the channel frequency of 1000 cycles is modulated, and the carrier in turn is modulated by this combination. The control impulses transmitted to the trafilc rails each one-half second interval that the output circuit is connected with the inductor coils by thecoder N will consist of the upper side band frequency of 8020 cycles. Such an impulse when picked up at the caboose will be applied to its input circuit, causing the two synchronizing relays 95 and IIII to be picked up and also causing a current of 20 cycles to appear in the output of the associated amplifier detector A3. Relay H2 will respond to this 20 cycle current and the running condition of the auxiliary brake controlling mechanism will be established, At the end of the one-half second interval of this impulse the coder N transfers the inductor coils on the locomotive from the transmitting circuit to the receiving circuit. The relays 95 and [DI on the caboose will now function to transfer its inductor coils from its receiving circuit to its transmitting circuit and a return impulse consisting of the carrier double modulated by the channel frequency of 1000 cycles and the signaling frequency of 30 cycles willbe supplied to the traflic rails. This return impulse consisting of the upper side bandfrequency of 8030 cycles will be picked up at the locomotive, filtered, demodulated, amplified and detected, causing to appear in the output of the associated amplifier detector A3 a current of 30 cycles, and the relay 82 will be energized. Relay 82 on picking up will cause the signal lamp 86 to be displayed to indicate to the locomotive operator that the impulse transmitted from the locomotive has been received at the caboose and that the apparatus at that location is in working order. As long as the handle 5 remains in the running or release position, these control and return impulses will be alternately exchanged between the two locations with the result that the running condition of the auxiliary brake controlling mechanism will be maintained in effect and the signal lamp 86 on the locomotive will be displayed.

In the event the locomotive operator moves" his brake valve handle 5 to either the service or emergency position, the signal frequency generated on the locomotive is shifted from 20 cycles to 40 cycles and the side band frequency is shifted from 8020 to 8040 cycles. The impulses now picked up at the caboose will cause to appear in the output of the amplifier detector A3 current of 40 cycles and the relay H5 will be energized and an automatic brake application will be efiected. The return impulses transmitted from the caboose will still contain the signal frequency of 30 cycles and hence the signal lamp 86 on the locomotive will remain displayed indicating to the locomotive operator that the control impulses are being received at the caboose and that the apparatus at that vpoint is in working order. Should the operator shift his handle 5 to the lap position, the channel frequency will be modulated at the signal frequency of 30 cycles and the side band transmitted will consist of 8030 cycles. This impulse when picked up at the caboose will cause to appear in the output of the amplifier detector a current of 30 cycles and the relay H4 will be energized with the result that the lap condition of the auxiliary brake controlling mechanism will be established. Again, the return impulses will contain the signal frequency of 30 cycles and the signal lamp 86 will still be displayed. It is to'be seen, therefore, that the automatic control will be effective to cause the condition of the auxiliary brake controlling mechanism to register with the position of the engineers brake valve and in each position an indication will be provided on the locomotive informing the operator that the system is operating properly.

If the train is to operate on a channel frequency other than 1000 cycles, each operator will set his selector SI at one of its other positions, the two selectors being set at corresponding positions so that the equipment at each location will operate on the same channel frequency. In the form of my invention here disclosed five different channel frequencies are available and hence five different trains can be operated on the railway with each train provided with a noninterfering control system. It is clear that the selectors can readily be provided with additional positions and additional condensers having different capacities connected therewith with the result that other trains could be provided with loud speaker on the locomotive.

Y speaker.

a distinctive channel frequency should it seem desirable to do so.

Since ordinarily an automatic volume control is used in the amplifier Al, the input energy to the amplifier detector A3 is substantially the same no matter which of the channel frequencies is used. The tuned circuit consisting of the reactor lil and the condenser selected by the contact member H can therefore be comparatively simple in construction. Thus, it is evident that the principle of double modulation of the carrier for obtaining a characteristicchannel frequency for each of a relatively large number of trains permits a comparatively simple filter arrangement.

I shall now assume that the operator on the locomotive desires to telephone to the operator in the caboose. The locomotive operator will first depress his push button PB, causing the generator GI at that location? to supply a signaling current of 10 cycles for modulating the channel frequency. The transmitted impulse will now contain a side band frequency of. 8010 cycles and the relay 'I it of the caboose apparatus will be picked up and the signal bell I26 will be sounded,

calling the caboose operators attention to the fact that telephone communication is desired. As pointed out hereinbefore, relay Ill when energized is effective to retain picked up whichever one of the control relays H2, I II and I It happens to be energized at the time and hence no change will take place in the condition of the brake controlling mechanism as the result of this signaling frequency of 10 cycles. The operator at the caboose will now shift his master switch MS to its No. 2 position and speak into his microphone M a prearranged remark that he is ready for telephone communication. In the meantime the 10- comotive operator shifts his master switch to its No. 3 position so that the remark transmitted from the caboose operator will be sounded by the From this point on the two operators will talk back and forth each shifting his master switch to either its No. 2 or No. 3 position according as to whether he is speaking into the microphone or is listening to the loud At the end of the telephone conversation each operator will release his master switch 'permittingit to return to its No. 1 position so that the automatic control will be at once reestablished. It is to be noted that the No. 2 and No. 3 positions of the master switch on the caboose will be effective to maintain the condition of the brake controlling mechanism during the telephone conversation.

In the event the caboose operator desires to telephone to the locomotive operator he will depress his push button PB causing the generator GI to supply a current of III cycles with the result that the return impulses now contain th side band frequency of 8010 cycles and the relay 4 on the locomotive will be energized. With the relay locomotive operator will now shift his master switch to its No. 2 position and speak the prearranged remark into the microphone M and the caboose operator will shift his master switch to its No. 3 position so thaLthis remark may be sounded on his loud speaker. From this point on telephone communication can be, carried on between the two operators in the manner described above.

Although definite frequencies have been set forth in the above description, it will be under- 2,089,795 stood that my invention is not limited to these 1. A signaling system for railway trains comprising the combination with a control device having different positions at one location on a train, a mechanism having different conditions at another location on the train, a communication circuit between said locations; of a transmitting means at said one location coupled with said circuit and including a source of carrier current, a receiving means at said other location coupled with said circuit and including a demodulator, a generator capable of supplying different channel frequencies, means governed by the different positions of the control device for modulating the output of said generator with different signaling frequencies, means for impressing the combined output of. the generator upon said carrier, a plurality of tuned circuits adapted to be connected with said demodulator and selectively responsive to the different channel frequencies, a.

means for governing the control device to establish the different conditions of said mechanism.

2. A signaling system for railway trains comprising the combination with a control device having different positions and a mechanism having different conditions at each of 'two locations on a train, a communication circuitbetween said locations and a transmitting. and a receiving means at each location alternately coupled with the circuit; of a source of carrier current for each transmitting means, a demodulator for each receiving means, a generator at each location capable of supplying different channel ,fre-

quencigs, means governed by the diiferent positions of each control device for modulating the output of the associated generator with diiferent signaling frequencies, means for impressing the combined output of the generator upon the carj rier, a group of tuned circuits connected with each demodulator and selectively responsive to the different channel frequencies, a detector connected with each group of tuned circuits, a plurality of signaling circuits controlled by each detector and selectively responsive to the differentsignaling frequencies, means governed by the signaling circuits for establishing the different conditions of the associated mechanism, a manually operated selector at each location for selecting a frequency of the generator and a tuned circuit at'itsrespective station to establish a characteristic channel frequency for the train, and a manually operated means at each location for g'overning'the control device to establish the different conditions of the at the other location.-

3. A signaling system for railway trains including, a communication circuit connecting two spaced locations on a train, a source of carrier current at one location coupled with said circuit, a generator adapted to generate different intermediate frequencies, a control device adapted to modulate the output of the'generator with different low frequencies, means for impressing the output of the generator upon the carrier to effect double modulation of said carrier, a receiving means at the other location coupled with the circuit and including a demodulator, a plurality of tuned circuits adapted to be connected with said demodulator and selectively responsive to different intermediate frequencies, a detector influenced by said tuned circuits, a plurality of control circuits controlled by the detector and selectively responsive to different low frequencies, a mechanism having different conditions governed by the control circuits, a manually operated selector at each location for selecting a corresponding intermediate frequency and tuned circuit at the two locations respectively, and a manually operated means for selecting the different low frequencies to influence a corresponding con trol circuit to establish a given condition of said mechanism, whereby a characteristic channel frequency can be selected for each of a plurality of different trains and each train equipped with a control system having a plurality of diiferent conditions.

4. A signaling system for railway trains including, a communication circuit connecting two spaced locations on a train, a source of carrier influenced by said tuned circuits, signaling means controlled by said detector and selectively re-s sponsive to said given low frequency, and a inanually operated selector at each location for selecting a corresponding intermediate frequency and tuned circuit at the two locations respectively whereby a signaling system having a characteristic channel frequency can be provided for each of a plurality of different trains.

5. A signaling system for railway trains including, a traflic track, a train, a source of carrier frequency current, a first generator adapted to supply different intermediate frequencies, a second generator adapted to supply different low frequencies, a control device having different positions for selecting the frequency of the second generator, a first manually operated selector having different positions for selecting the frequency of the first generator, means for double modulating the carrier with the outputs of said generators, means for suppressing the carrier and one side band, coding means for supplying periodic impulses of the remaining side band to the traflic track, receiving means mounted on the train in inductive relation with the traffic track and including a demodulator, a code following relay and a plurality of tuned circuits controlled by the demodulator, said circuits selectively responsive to the different intermediate frequencies, a second manually operated selector having different positions for selecting the tuned circuit corresponding to the selected frequency of the first generator, signaling circuits influenced by the selected tuned circuit selectively responsive to the different low frequencies, and means controlled by the code following relay for governing the receiving means.

6. A signaling system for railway trains including, a communication circuit connecting two spaced locations on a train, receiving and demodulating means at one location coupled with said circuit, a telephone receiver and a plurality of tuned circuits controlled by said demodulating means and selectively responsive to different mtermediate frequencies, a detector adapted to be influenced by any one of said tuned circuits, a plurality of control circuits governed by the detector and selectively responsive to different low frequencies, a mechanism having dififerent operating conditions selectively governed by said control circuits, a manually operated selector for selecting any one of said tuned circuits, a manually operated switch for connecting either the telephone receiver or the selected tuned circuit with said demodulating means, a source of carrier current at the other location coupled with said communication circuit, telephone means adapted to modulate said carrier with voice frequencies, a generator adapted to impress upon said carrier different intermediate frequencies, control means for modulating the Output of said generator with different low frequencies, a manually operated selector at said other location for selecting the frequency of said generator, a manually operated means for selecting the low frequency, and a manually operated switch for connecting either the telephone means or the generator with said carrier, whereby telephone communication or a control operating on a distinctive intermediate frequency for effecting the different conditions of the mechanism can be established between said two locations.

'7. A signaling system for railway trains including, a communication circuit connecting two spaced locations on a train, a source of carrier current at one location coupled with said circuit,

a telephone transmitter for modulating the carrier with voice frequencies, a generator adapted to supply different intermediate frequencies, control means adapted to modulate the output of said generator with different low frequencies, means for modulating the carrier with the output of said generator, a demodulator at said other location coupled with the communication circuit, a telephone receiver and a plurality of tuned circuits controlled by the demodulator, said tuned circuits selectively responsive to the diiferent intermediate frequencies, a detector influenced by said tuned circuits, a plurality of Signaling circuits controlled by the detector and selectively responsive to said different low frequencies, a manually operated selector at each location for selecting a corresponding intermediate frequency and tuned circuit at the two locations respectively, a manually operated means for selecting the different low frequencies for influencing' a corresponding signaling circuit, a manually operated switch at said one location for rendering active either the telephone transmitter or the generator, and a manually oper-' 'j tion or an automatic control can be established I,

between the two locations.

8. A signaling system for railway trains comprising the combination with the usual engineer's brake valve on the locomotive, an auxiliary brake controlling mechanism located at another point on the train adapted to reproduce different operating functions of the engineers valve and a communication circuit connecting. the two locations; of a source of carrier current, a generator adapted to supply any one of several different intermediate frequencies, means for modulating the output of said generator with different low frequencies according to the position of the en gineers brake valve, means for modulating the carrier with the output of said generator, means for supplying a side band of the double modulated carrier to said circuit, receiving means at said other location coupled with said circuit including a demodulator, a plurality of tuned circuits governed by the demodulator and selectively responsive to the different intermediate frequencies, control circuits governed by the tuned circuits and selectively responsive to the difierent low frequencies for causing the auxiliary brake controlling mechanism to register with the engineer's valve, and a manually operated selector at each of the two locations for selecting a corresponding intermediate frequency and tuned circuit respectively whereby a channel of a characteristic frequency can be provided for each of several trains.

9. A signaling system for railway trains comprising the combination with a source of carrier current, a telephone receiver, a telephone transmitter, a signaling device having different positions and a control device having different positions at each of two spaced locations on a train; of a first generator at each location adapted to supply different frequencies within the voice frequency range, a second generator at each location adapted to modulate the output of the first generator with different low frequencies according to the position of the control device, transmitting means at each location for modulating the carrier with the combined output of the first generator and then suppressing the carrier and one side band, receiving means at each location responsive to such transmitted side band and including a demodulator, a plurality of tuned circuits adapted to be connected with each demodulator selectively responsive to the frequencies of said first generator, signaling circuits governed by the tuned circuits for controlling the signaling device and selectively responsive to the different low frequencies, coding means partly at each location for automatically exchanging impulses of the transmitted side hand between the two locations for causing the signaling device at each location to register with the position of the control device at the other location, a manually operated selector at each location to select a corresponding frequency of the first generator and tuned circuits for establishing a characteristic channel frequency for the train; and a manually operated master switch at each location for rendering the coding means, first generator and tuned circuits ineffective and for connecting the telephone transmitter and receiver with the carrier source and demodulator respectively for establishing tele-' phone communication.

10. In combination with a railway having a plurality of railway trains, a signaling mechanism for each train having a plurality of different positions; and a non-interfering control system for controlling the signaling mechanism of each train including, a source of carrier current, a generator adapted to supply different channel frequencies, control means for modulating the output of said generator with different low frequencies corresponding to the different positions of the signaling mechanism, means for modulatw ing the carrier with the combined output of the generator and then suppressing the carrier and one side band, receiving means influenced by the remaining side band, a demodulator con-' trolled by the receiving means, a plurality of tuned circuits adapted to be connected with the demodulator and selectively responsive to the different channel frequencies, signaling circuits governed by the tuned circuits selectively responsive to the different low frequencies for causing the signaling mechanism to register with said control means, and selecting means for establishing a corresponding channel frequency and tuned circuit.

ANDREW J. SORENSEN. 

